1. Field of the Invention
This invention relates to an apparatus for improved acoustic monitoring of the cardiac pulse while simultaneously administering anesthetic gases to a patient during surgery.
2. Description of the Prior Art
During operations in which general anesthesia is used, the accepted practice is to administer the anesthetic gases through a flexible endotracheal tube which is inserted through the mouth of the patient and into the trachea. The early, rudimentary versions of such an endotracheal tube were greatly improved by the addition of sealing means at the outside of the distal end of the tube. The sealing means in most common usage today comprises an inflatable cuff which can expand into contact with the interior wall of the trachea. With trachea thus blocked, positive control over the administration of anesthesia and of the respiration itself is permitted through the respiratory passage in the endotracheal tube.
The administration of anesthesia gases tends to produce a state of relaxation of muscle tissue. This effect is quite desirable to the surgeon who must cut into and through such tissue, but it also can have effects which are not desired. Although some of the undesired effects may not be evident until the post-operative recovery period, the possibility of cardiac arrest is typically of utmost concern during the surgery itself.
Since cardiac arrest is an ever-present danger during the condition of general anesthesia, the cardiac pulse must be monitored carefully and continually. In fact, in some states there exists practically an absolute requirement to monitor the actual heart sounds during surgical procedures. In other areas, the amount and type of cardiac monitoring is left to local or hospital rule, or to the preference of the anesthesiologist. Sometimes, such monitoring is accomplished acoustically as by taping an acoustic stethoscope pickup directly to the exterior of the body of the patient in the region of the chest. Such cardiac monitoring is perhaps more often accomplished by electrical or electronic means which essentially monitor motor nerve impulses. The electrical activity thus picked up is usually converted into audible "beeps" which essentially serve only to monitor the heart rate, and occasionally the same electrical activity may be presented for visual observation on an oscilloscope. This direct technique of electrical monitoring of motor nerve impulses is often remarkably less sensitive than acoustic monitoring of the cardiac pulse, and in addition the audible "beeps" produced by electrical monitoring are far less informative of the actual activity and condition of the heart than the true heart sounds available through acoustic monitors. By listening to the actual heart sounds through acoustic monitoring means the anesthesiologist can receive the earliest possible indication that the heart is becoming depressed due to the anesthetic, thus permitting the anesthesiologist to take early and minimal corrective measures so that there is little or no impact on the progress of the surgical procedure and no adverse effect on the patient.
Acoustic monitoring of the heart during surgery has been accomplished by using one or more acoustic pickups for stethoscopes taped to the chest of the patient. However, even under the best of conditions, the heart sounds are attenuated substantially by the body tissue in the sound path from the heart to the acoustic pickup, and it is often impossible to change the location of the stethoscope acoustic pickup once the surgical procedure has begun. This type of acoustic monitoring on the outside of the chest wall is particularly difficult and unsatisfactory for obese patients, since the excessive amount of body tissue in the sound path between the heart and the acoustic pickup often attenuates the heart sounds to an unusable level.
Although the present invention is generally oriented toward cardiac monitoring during surgery, is also applicable to the carefully monitoring of the cardiac pulse which may also be required for several days after surgery while the patient is in the intensive care unit. Endotracheal monitors are well suited to such prolonged use.
The nature of the surgery permitting, one of the preferred cardiac pulse monitoring methods requires the use of a device known as an "esophageal tube", which, as its name implies, is inserted in the esophagus of the patient. Acoustic or electric sensors may be disposed near the distal end of the esophageal tube to pick up and transmit the cardiac pulse from the surrounding tissue. Unfortunately, the amount of various body fluids in the esophagus can vary drastically during the course of surgery; such variations not only can affect the ability to monitor the cardiac pulse acoustically, but can also create confusing and distracting noise. The esophageal tube itself must be sealed at its distal end in order to prevent the entrance of body fluids which may occasionally be present in the esophagus during surgery. Also, sensors located in the esophagus cannot always be positioned as close to the heart as is possible with sensors located at the distal end of an endotracheal tube. Thus esophageal sensors tend to distort the cardiac pulse. A more reliable means of monitoring the cardiac pulse with greater fidelity is desirable.
The esophageal tube has the disadvantage of being difficult to locate properly in some situations. In attempting to properly place the esophageal tube, it is possible for the anesthesiologist to perforate the wall of the esophagus resulting in "false passage". Such false passage is more likely to occur where there is scar tissue in the esophagus or where there is a congenital pouch in the wall of the esophagus which leads the probing tip of the esophageal tube in the wrong direction. Due to the nature of the tissue involved, false passage is a less significant problem in the trachea than in the esophagus. Since an endotracheal tube is used in most cases for the administration of the anesthetic gases, the use of a separate esophageal tube merely for the purpose of monitoring the cardiac pulse creates excessive and unnecessary crowding in the area of the mouth of the patient, and adds unnecessary expense to the surgical procedure itself. Also certain forms of radical neck surgery involving the esophagus would necessarily preclude the use of an esophageal stethoscope in any form.
Even where esophageal stethoscopes are used routinely, it is difficult to adequately seal the esophagus to prevent fluids from the digestive track from moving toward the mouth of the patient during the operation. Depending somewhat upon the nature of the surgery and the length of the operation, these fluids may find their way into the trachea of the patient, and ultimately into the lungs of the patient. Such leakage of fluids from the esophagus into the trachea can cause aspiration pneumonia, which is a problem commonly associated with the use of esophageal stethoscope tubes.
Current monitoring devices which convert sound into an electrical signal for transmission to the output means are generally deficient in two respects. First, the output is often limited to a series of gated tone bursts commonly known as "beeps". Such a signal provides only an indication of the cardiac rate, and actually serves to conceal the degree of depression of the heart during surgery. In those systems where additional information containing more of the actual heart sound is used, the deficiency arises from the fact that the output is generally available only to the anesthesiologist, and not to the surgeon(s) operating on the patient.
Thus, it is desirable to monitor the heart sounds acoustically via a trachea tube. However, these heart sounds must be transmitted via an axial canal separate from the respiratory canal. When this is attempted, however, several major problems occur. One such problem is the amount of space available in a patient's trachea. The tracheal tube must have a relatively large opening passage in order to provide enough air to the patient and thus tube uses much of the space available in the patient's trachea. In addition, since the respiratory tube is sealed at its distal end, the second acoustical tube would be blocked by the seal. Also, if two tubes were to be used they could rub on each other causing extra sounds and confusion. Another mechanical problem is the placement of the two tubes. The large respiratory tube is relatively easy to insert. The smaller acoustical tube, however, would tend to wander around and be relatively uncontrollable.
Thus, the solution is directed to a combination of the two tubes into one tube. This, in turn, has several problems. As discussed, the main respiratory tube canal must have a relatively large diameter in order to control the respiratory process. The wall thickness around the canal must be pliable enough to conform to the trachea passage. This argues for a thin walled tube. The outside wall must be smooth for easy and unobstructed passage. On the other hand, the acoustic canal must be large enough to allow acoustic wave forms to pass unmodulated so that enough sound energy can pass from the patient to avoid sound tapes. In addition, the two canals must be acoustically separate.
Therefore, it is an object of this invention to provide an apparatus which overcomes the aforementioned inadequacies of the prior art devices and provides a significant improvement to the advancement of the prior art.
Another object of this invention is to provide a flexible endotracheal tube with an inflatable cuff suitable for sealing the trachea and having means for permitting the monitoring of pressure variations within the inflated cuff.
Another object of this invention is to provide a dual canal tracheal tube constructed to conform to the tracheal passage allowing a maximum opening for both canals while still providing acoustical separation and a smooth, no crevice, outside perimeter.
Another object of this invention is to provide a flexible conduit to conduct pressure variations from an inflatable cuff on the distal end of an endotracheal tube to an external monitor connector.
Another object of this invention is to provide a diaphragm-sealed connected in the pressurization conduit system of an endotracheal tube having an inflatable cuff so that sounds transmitted through the tracheal wall to the inflated cuff may be monitored externally while maintaining the pressure integrity of the inflated cuff and conduit system.
Another object of this invention is to provide an endotracheal cardiac monitor so that only one tube is required to be inserted into the mouth of a patient during surgery thus reducing crowding in the vicinity of the mouth of the patient as well as reducing the expense of equipment required for surgery.
Another object of this invention is to provide an electromechanical transducer to convert the pressure variations representing heart sounds into an electrical signal suitable for processing and specific distribution.
Another object of this invention is to provide an output means wherein the electrical signal representing the heart sounds is displayed on a video display and on a chart recorder, as well as being made available as an audio output either to headphones or to a loudspeaker.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed to be merely illustrative of some of the more pertinent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description describing the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.